Inkjet printers have a series of nozzles from which individual ink droplets are ejected to deposit on print media to form desired printed images. The nozzles are incorporated in various types of printheads and their proper functioning is critical to the creation of quality images. Thus, any partial or total blockage of even a single nozzle may have a significant impact on a printed image, particularly in the case of a pagewidth printer.
The nozzles are prone to blockage due to their exposure to ever-present paper dust and other particulate matter and due to the tendency of ink to dry in the nozzles during, often very short, idle periods. Prior to ejection, the ink forms a meniscus at the nozzle opening. Exposure to air (frequently warm) evaporates the ink solvent to leave a solid deposit that can block the nozzle.
Servicing systems are conventionally employed for maintaining the functionality of printheads. Such systems provide capping, purging and or wiping. Capping involves the covering of idle nozzles to preclude exposure of ink to drying air. Purging is normaly effected by evacuating a capping chamber, thereby sucking deposits from the printhead that block or have the potential to block the nozzles. Wiping is performed in conjunction with the capping and/or purging functions and involves gently sweeping a membrane across the face of the printhead.
Most conventional inkjet printers use a reciprocating printhead which is traverses across the width of a momentarily stationary page or portion of print media. In these printers, service stations are provided at one side of the printing zone and, on command, the printhead is traversed to the service station where it is docked while servicing is performed and or the printer is idle.
The above described servicing system is not feasible for pagewidth printers because of the stationary printhead assembly that extends across the full width of the printing zone. The printhead assembly effectively defines the print zone and it cannot be moved outside of that zone for servicing. Furthermore, a pagewidth printhead has a significantly larger surface area and contains a vastly greater number of nozzles than a conventional inkjet printhead, especially in the case of a large format printer. These factors dictate that the servicing of printheads requires an entirely different approach to that of conventional scanning type printheads.